Rust 字段的默认值
示例
extern crate serde;
extern crate serde_json;
#[macro_use] extern crate serde_derive;
#[derive(Deserialize, Debug)]
struct Request {
// Use the result of a function as the default if "resource" is
//不包括在输入中。
#[serde(default="default_resource")]
resource: String,
//使用类型的std::default::Default的实现，如果
// "timeout" is not included in the input.
#[serde(default)]
timeout: Timeout,
// Use a method from the type as the default if "priority" is not
//包含在输入中。这也可能是特征方法。
#[serde(default="Priority::lowest")]
priority: Priority,
}
fn default_resource() -> String {
"/".to_string()
}
///超时（以秒为单位）。
#[derive(Deserialize, Debug)]
struct Timeout(u32);
impl Default for Timeout {
fn default() -> Self {
Timeout(30)
}
}
#[derive(Deserialize, Debug)]
enum Priority { ExtraHigh, High, Normal, Low, ExtraLow }
impl Priority {
fn lowest() -> Self { Priority::ExtraLow }
}
fn main() {
let json = r#"
[
{
"resource": "/users"
},
{
"timeout": 5,
"priority": "High"
}
]
"#;
let requests: Vec<Request> = serde_json::from_str(json).unwrap();
// The first request has resource="/users", timeout=30, priority=ExtraLow
println!("{:?}", requests[0]);
// The second request has resource="/", timeout=5, priority=High
println!("{:?}", requests[1]);
}
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